The present invention relates to a variable-valve-actuation (VVA) apparatus for an internal combustion engine that can vary, particularly, the lift amount of valves such as intake valve and exhaust valve in accordance with engine operating conditions.
The VVA apparatus typically comprises an eccentric rotary (ER) cam fixed to a driving shaft for rotation therewith, a pivotal valve operating (VO) cam, a rocker arm having a first arm and a second arm, a control rod or shaft having an eccentric control cam, and a crank arm. The eccentric control cam supports the rocker arm for pivotal motion. The crank arm interconnects the ER cam and the first arm of the rocker arm. A link interconnects the second arm of the rocker arm and the VO cam.
The VVA apparatus is constructed to change a rocking fulcrum of the rocker arm in accordance with the rotating position of the control cam to obtain variable valve-lift characteristic. However, no consideration is given to rotation control of the control cam, i.e. a load acting on the control shaft during rotation thereof. As a consequence, a load on an actuator for driving the control shaft becomes greater to produce greater driving energy. This leads not only to an increase in size of the actuator, but to a possible degradation of power consumption for the actuator and fuel consumption for the engine.
It is, therefore, an object of the present invention to provide a VVA apparatus for an internal combustion engine, which contributes to the optimization of power consumption for the actuator and fuel consumption for the engine without increasing a size of the actuator.
The present invention generally provides a VVA apparatus for an internal combustion engine, comprising:
a driving shaft that rotates in synchronism with a crankshaft;
a crank cam arranged at an outer periphery of the driving shaft;
a VO cam swingably supported by the driving shaft, the VO cam actuating an engine valve; and
a rocker arm having a first arm swingably mounted to an eccentric control cam at a first pivotal point and a second arm rotatably mounted to the crank cam and the VO cam at a second pivotal point and a third pivotal point, respectively, the rocker arm transmitting a driving force of the crank cam to the VO cam,
wherein a lift of the engine valve produced by the VO cam is varied by changing a rocking fulcrum of the rocker arm through rotation control of the control cam, and
wherein the second pivotal point and the third pivotal point are located on the side of the second arm of the rocker arm.